SIP packets blocked by firewall as "bad NAT"

Hi,

I'm using m0n0wall 1.33 generic PC. The firewall is blocking SIP 
packets, no matter if I open port 5060 or forward it to my VoIP phone. 
Firewall log entries look like that:

15:18:10.352452 bge0 @0:25 b <IP of VoIP provider>,5060 -> 10.3.0.2,5060 
PR udp len 20 32 IN bad NAT

I found this resolved topic, where Manuel Kasper wrote he fixed it: 
http://forum.m0n0.ch/index.php?topic=2423.0 
<http://forum.m0n0.ch/index.php/topic,2423.0.html>.

Is there something I'm doing wrong? Could it be the Broadcom NIC: 
http://gnats.netbsd.org/30851

Thank you!
tonabnehmer
<http://gnats.netbsd.org/30851>